298 DIPTERA. 
Lucy, Then all the common black 
flies are in this order r 
Mother, Yes, all ; and a vast va- 
riety of others. Dipterous flies have 
two kalteres*^ orpoisers; and these ap- 
pendages are peculiar to them. 
Lucy. What are hal teres, mamma ? 
Mother, They are little knobs, at the 
end of short pedicles, and are something 
like the stamens of a flower. The knobs 
are supposed to be hollow, as it were 
little bladders filled with air. There are 
two of them, one placed under each 
wing. 
Lucy. What can be the use of these 
little things ? 
Mother. Naturalists do not seem to 
have decided this point : some think, that 
they assist the fly to balance itself, and 
for that reason they have been called 
poisers ; and others imagine that the 
buzzing sound, made by flies when on 
the wing, is produced by these organs. 
* Weights held by ropedancers, as counterpoises. 
